This invention relates generally to ink jet printing apparatus and more particularly to the ink return system for intercepting and recovering the unused ink.
Ink return systems for intercepting and recovering unused ink have been widely utilized in ink jet printing systems. The systems usually include a catcher which initially catches ink and then dumps it into a conduit for eventual return to the ink supply system reservoir to be reused. Ink is scavenged from the catcher entryway by connecting the conduit to a vacuum source. The establishment of a vacuum in the conduit not only draws ink away from the entryway but also draws it through the conduit and into a return tank. The vacuum level is commonly adjusted to a sufficiently high level so that air drawn into the catcher from the surrounding area also draws the ink mist that commonly exists about the catcher into the entryway. It is desirable that the ink mist be pulled into the catcher so as to prevent its deposition either on adjacent components of the printing system or the printing surface.
For certain applications of ink jet printing it is necessary to use inks that are solvent based, for example alcohol or ketone based. These inks suffer relatively high evaporation rates when exposed to air. It is while using those inks and maintaining the high level air flow in the catcher area that solvent evaporation occurs at a rapid rate. The loss of solvent by the ink eventually causes it to become unusable, and then it has to be replaced or reformulated.
To reduce evaporation of solvent in the ink return system the prior art has used an ink separator as disclosed in Arway et al. U.S. Pat. No. 4,023,182, assigned to A. B. Dick Company, assignee of the present application. Interposing an ink/air separator between a catcher, ordinarily a part of the print head, and an ink return tank substantially increases the time period over which the ink formulation remains within acceptable operational limits. The separator, however, does not reduce the high rate of air flow in the catcher where ink is captured. Also, it is necessary to provide a mounting for the separator near the ink jet print head oriented suitably so that gravity can be utilized to separate the ink from the ink-air mixture entering the separator.